diff --git a/packages/ui/src/components/session-turn.tsx b/packages/ui/src/components/session-turn.tsx
index 9ffa671e6985..c5cea43bf092 100644
--- a/packages/ui/src/components/session-turn.tsx
+++ b/packages/ui/src/components/session-turn.tsx
@@ -378,6 +378,17 @@ export function SessionTurn(
 
   const isShellMode = createMemo(() => !!shellModePart())
 
+  const hasReasoningParts = createMemo(() => {
+    for (const m of assistantMessages()) {
+      const msgParts = data.store.part[m.id]
+      if (!msgParts) continue
+      for (const p of msgParts) {
+        if (p?.type === "reasoning") return true
+      }
+    }
+    return false
+  })
+
   const rawStatus = createMemo(() => {
     const msgs = assistantMessages()
     let last: PartType | undefined
@@ -509,6 +520,8 @@ export function SessionTurn(
     retrySeconds: 0,
     status: rawStatus(),
     duration: duration(),
+    userMessageHovered: false,
+    showReasoning: false,
   })
 
   createEffect(() => {
@@ -730,7 +743,7 @@ export function SessionTurn(
                               message={assistantMessage}
                               responsePartId={responsePartId()}
                               hideResponsePart={hideResponsePart()}
-                              hideReasoning={!working()}
+                              hideReasoning={!working() && !store.showReasoning}
                               hidden={hidden}
                             />
                           )}
@@ -758,6 +771,22 @@ export function SessionTurn(
                         <div data-slot="session-turn-summary-header">
                           <div data-slot="session-turn-summary-title-row">
                             <h2 data-slot="session-turn-summary-title">{i18n.t("ui.sessionTurn.summary.response")}</h2>
+
+                            <Show when={hasReasoningParts()}>
+                              <Button
+                                data-slot="session-turn-thinking-toggle"
+                                variant="ghost"
+                                size="small"
+                                onMouseDown={(e: MouseEvent) => e.preventDefault()}
+                                onClick={(event: MouseEvent) => {
+                                  event.stopPropagation()
+                                  setStore("showReasoning", (prev) => !prev)
+                                }}
+                              >
+                                {store.showReasoning ? "Hide thinking" : "Show thinking"}
+                              </Button>
+                            </Show>
+
                             <Show when={response()}>
                               <div data-slot="session-turn-response-copy-wrapper">
                                 <Tooltip
@@ -780,6 +809,7 @@ export function SessionTurn(
                               </div>
                             </Show>
                           </div>
+
                           <div data-slot="session-turn-response">
                             <Markdown
                               data-slot="session-turn-markdown"